Garry’s Mod – ACF Gear Tuning for Performance!

Introduction

Your ACF vehicle might be powerful, but a lot of its potential can be lost due to improperly adjusted gears. They might be too short and you reach your top speed too early, or they might be too long and you overload your engine. Another common mistake is that the whole power band of an engine is not used.
This tutorial proposes a gear tuning method for ACF vehicles to achieve their maximum top speed with the biggest acceleration.

Test Ground

First, you must find a drag s*rip with enough runway, such as the gm_carcon_ws one. You can use other maps too, just make sure there is a long straight where you will be able to reach the maximum speed of your vehicle.

Make Differential Ratios 1

Before you do any adjusting, update your differentials to have gear ratios and final drives equal to 1, this will help make the calculations easier in the future. You can leave the gearbox final drive on 0.5, which is probably the most optimal.

Adjust Gears So Its Drivable

Once you have updated all your final drives to 1, the car will probably be very sluggish. You must now decrease all the gear ratios so the car accelerates at all. Try run it to the end of drag s*rip with full RPM in each gear and see if you can reach the last gear. If not, decrease the gears again.

Find the Top Gear

Now that your car accelerates decently enough, your aim is to find the perfect gear ratio of the last gear. Take a look at your engine and check for the power band.
I will now use an example, my engine has a powerband 5750-8500 and I have 5 gears. I memorize the power band max RPM which is 8500 in my case.
Every car with drag will have some kind of a maximum top speed, your goal is to adjust the last gear so the car stops accelerating almost exactly at end of power band, in my case 8500.

My example:
1. I have set the 5th gear to 0.37 and I reach top speed at 7500 RPM. This means I must now make the 5th gear ratio smaller, for example 0.33, and try again.
2. I have set the 5th gear to 0.33 and I reach top speed at 8900 RPM. This means I must now make the 5th gear ratio bigger, for example 0.34, and try again.
3. I have set the 5th gear to 0.34 and I reach top speed at 8600 RPM, which is practically perfect!
4. I adjust the 5th gear ratio to 0.35 and I reach top speed at 8400 RPM, this gives me a bit of room for error and I always stay in my power band. I have found my perfect 5th gear ratio – 0.35.

Calculate the Other Gears

Now that you have found the perfect last gear, you can calculate all the other gears.
You must now get a power band ratio. My power band is 5750-8500, so the power band ratio (PBR) is:
PBR = 5750 / 8500 = 0.676
This ratio will then determine the difference in my gears. This is the theoretical perfect, but I might fail to switch gears perfectly every single time, so I round it up to about 0.7 to account for that.

Now I calculate my gears as follows:
5th gear = 0.35 (from before)
4th gear = 0.35 * 0.7 = 0.245 ~ 0.25 (It is best to round these values up)
3rd gear = 0.25 * 0.7 = 0.175 ~ 0.18
2nd gear = 0.18 * 0.7 = 0.126 ~ 0.13
1st gear = 0.13 * 0.7 = 0.091 ~ 0.10

So now I have gotten all my gears:
1. 0.10
2. 0.13
3. 0.18
4. 0.25
5. 0.35

Gear ratios like these make sure when you switch to next gear at maximum power band RPM, your RPM will drop to the minimum power band RPM. This makes sure you accelerate to your top speed by using the entire engine power band.

Adjust Gear Placement

If you did exactly as shown, chances are your 1st and 2nd gears will feel very short and useless. In this case you can simply remove the shorter gears and shift the upper gears downwards. In my example it will make the 3rd gear my top speed gear.

My example:
1. 0.10 0.18
2. 0.13 0.25
3. 0.18 0.35
4. 0.25 0.40 (These are overdrive gears and don’t matter, you can put whatever you want here)
5. 0.35 0.45

Generally you want your 1st gear not to make excessive wheel-spin, but also to not overload the engine. Every car will be different – some will need all 5 gears, some will need only 2 for top speed.
The reverse gear is totally up to you, but I usually set it 0.01 bigger than the 1st gear. My gearbox now would look like this:
1. 0.18
2. 0.25
3. 0.35
4. 0.40
5. 0.45
R: -0.19
FD: 0.5

Conclusion

Generally you want to tune your gears when you know the car will not change its weight or any other properties. If you want to change the final drive, you have to recalculate all the gear ratios from start.

I hope this was helpful and most importantly – Good Luck! 🙂

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